There is no easily performed and specific assay for primary biliary cirrhosis (PBC) available commercially to the clinical laboratory. Antibodies to the mitochondrial antigen M2 have been shown to be a sensitive and specific marker for this disease. We are proposing a microwell enzyme immunoassay (EIA) for the detection of human antibodies to M2 antigen in serum or plasma. This will be a useful aid in the early diagnosis of PBC, which in turn is related to prolonged patient survival. The EIA test will be simple, rapid, highly sensitive and specific for PBC. The test format will be flexible inasmuch as it will be ideally suited either for smaller laboratories using manual techniques, or larger reference laboratories with fully automated instrumentation. Phase I efforts will be devoted to the isolation of the M2 antigen from mitochondria, preliminary formulation of the EIA reagents and procedure, and small scale clinical evaluation. Phase II will include production of M2 antigen by recombinant techniques, final formulation of the EIA reagents and test procedure with mitochondrial or recombinant antigen, and full- scale clinical evaluation with appropriate patient populations.